In the treatment of patients it is often desirable to provide a means whereby a drug or like agent can be introduced in a controlled manner over an extensive period of time. With the conventional intake of drugs and the like by means of periodic ingestion of a capsule or tablet, or periodic injection, there is usually an initial significant increase in the amount of the active agent in the body which is then reduced over a period of time, until the next tablet is taken or injection given.
In many cases it is preferable to provide an intake of drug in a controlled manner such that the amount of drug in the body remains substantially constant. This is particularly the case in the treatment of patients suffering constant pain as in the case of terminally ill patients who require a constant amount of an analgesic to be administered in order for them to be able to withstand the pain.
In the past several devices have been proposed for controlling the introduction of the drug into a body whereby it can be delivered in a controlled manner over a period of time. Such devices have comprised pumps driven by a power source, which controls the delivery of drug to the body. Some of these pumps may be mounted externally to the body and are connected to a catheter introduced to a the body of the patient. Other devices have comprised a pump which is mounted subcutaneously to the body of the patient and which delivers a drug to the body at a desired location. Such devices suffer the disadvantage however they are quite expensive and that they utilise a power source in order to effect the delivery of the drug. In the event of the failure of the power source, the pump must be replaced. The power source has in the past taken a variety of forms including utilisation of a phase-change fluid as is the case of a device marketed under the trade mark xe2x80x9cINFUSAIDxe2x80x9d.
Other delivery devices have comprised a manually operated pump which may be mounted externally to the body or subcutaneously in the body of the patient whereby the pump can be activated by the patient for the delivery of the drug as need arises for that drug. Examples of such devices are disclosed in U.S. Pat. Nos. 4,588,394, 4,681,560 and 5,085,644 the contents of which are included herein by reference, and comprise devices whereby a pumping chamber is connected via catheter directly into the body and derives its source of drug from a holding reservoir. The pumping chambers are of the form whereby they are biased to a maximum volume condition, and on activation by the patient it is moved to a minimum volume position. In the case of 5,085,644 the re-entry of the drug into the pumping chamber is controlled by means of a capillary such that the pump is only able to deliver a full volume after a predetermined period of time. However, the disadvantage with this form of delivery means is that drug levels within the body will vary periodically whereby on activation of the pump, the drug level within the body initially has a high level which is then allowed to decay over a period of time until the pump is reactivated.
It is an object of this invention to provide a drug delivery means whereby the delivery of the drug to the patient can be controlled in order that there is a generally constant delivery of the drug for a period of time without the need for any form of power source. According to the invention there will be some variation in the flow rate but in comparison to the magnitude of the flow rate the variation is not significant in regard to the desired administered rate of the drug. It is an object of the invention to maintain the delivery rate within the range of desired administration rates for the drug being administered.
Accordingly the invention resides in a drug delivery means comprising a holding reservoir, a pump, a delivery reservoir and an outlet, said holding reservoir being connected to said delivery reservoir through said pump, said pump being operable manually whereby fluid is transferred from the holding reservoir to the delivery reservoir, said delivery reservoir being connected to the outlet through a flow restriction means which controls flow to the outlet, said delivery reservoir being formed to be resiliently expandable from a minimum volume to a maximum volume whereby the pressure induced on the fluid within the delivery reservoir between a first volume and a second volume is generally constant where the first volume is greater then the second volume and wherein the connection between the holding reservoir and the delivery reservoir permits flow only from the holding reservoir to the delivery reservoir while the pressure within the delivery reservoir is less than a predetermined pressure, said connection having a control means for preventing further delivery of fluid from the pumping means to the delivery reservoir on the pressure within the delivery reservoir attaining a predetermined pressure.
According to a preferred feature of the invention the first volume is equal to the maximum volume.
According to a preferred feature the first volume is less than the maximum volume.
According to a further preferred feature the second volume is equal to the minimum volume.
According to a further preferred feature the second embodiment is greater than the minimum volume.
In one form the control means comprises a first valve between the holding reservoir and the pump, and a second valve between the pump and the delivery reservoir, said first and second valves permitting unidirectional flow to the pump and delivery reservoir respectively when said delivery reservoir is not filled to its maximum volume and the pressure within the delivery reservoir is less than the predetermined pressure, the second valve permitting flow to the holding reservoir while the pressure within the delivery reservoir is at least equal to the predetermined pressure.
According to an alternative form the control means incorporates a unidirectional flow first valve between the holding reservoir and pump and a relief chamber between the pump and the delivery reservoir, said relief chamber being resiliently expandable with the expandable portion of the wall of the chamber having a higher modulus of elasticity than the delivery reservoir whereby the expandable portion will expand on the pressure between the pump and delivery reservoir being at least equal to the predetermined pressure.
In another form the control means may comprise a relief valve located between the delivery reservoir and the holding reservoir which will permit flow from the delivery reservoir to the holding reservoir when the fluid pressure in the delivery reservoir is at least equal to the predetermined pressure.
According to a preferred feature the flow restriction means comprises a single passageway and a filter located upstream from the passageway.
According to a preferred feature of the invention the flow restriction means is formed with a plurality of flow pathways. In one form the flow restriction means may comprise a plurality of capillary passageways. In one form the flow restriction means comprises a porous element. The porous element can be formed of glass, ceramic or a like inert material.
According to a further preferred feature a control valve is mounted between the delivery reservoir and the outlet, said control valve being adapted to open to allow fluid flow to the outlet on the pressure on the delivery reservoir exceeding a preset pressure wherein the preset pressure is less than the maximum. According to one embodiment the preset pressure is substantially equal to the pressure induced on the fluid in the delivery reservoir when the delivery reservoir is at its second volume. According to another preferred feature a bypass line is provided between the inlet and outlet of the control valve and a second flow restriction as provided in the bypass line.
The invention would be more fully understood in the light of the following description of several specific embodiment. The description is made with reference to the accompanying drawings of which: